But now that it's President Obama calling on Romney to release more than two years of returns, Gingrich told CBS News that the demand "comes across as hollow."

If anything, it's Mr. Obama who isn't being transparent, he contended. "This is a president who hasn't even released his undergraduate stuff at Columbia... used executive privilege in Fast and Furious... They're like a lawyer with a bad case," he said.

Gingrich released his 2010 tax return hours before the January 19 debate. At the time, Romney hadn't released any of his own returns, promising in the debate, "I'll release multiple years. I don't know how many years. And -- but I'll be happy to do that." He's so far released his 2010 return and an estimate of his 2011 return.

Gingrich told CBS that two years' worth of returns should be enough -- and that there's no incentive for the candidate to release more.

"If he releases 15 years, the New York Times and the Washington Post will assign people to go through every single page, and you're going to get 35 days of page-one stories, all of them misleading," he said.

Ultimately, Gingrich said, voters will be more concerned with the way Mr. Obama's economic policies have impacted their own finances. "In the end, the American people care more about their own tax return than Mitt Romney's."